System for flare gas recovery using gas sweetening process

ABSTRACT

A flare gas recovery system includes a primary gas sweetening unit; and a liquid-driven ejector in continuous fluid communication with the primary gas sweetening unit. The ejector includes an inlet configured to receive a motive fluid including a regenerable amine solvent in a rich state from the primary gas sweetening unit; a gas inlet configured to receive a suction fluid including a gas; and a fluid outlet configured to either directly or indirectly discharge to the primary gas sweetening unit a two-phase fluid including a mixture of the suction fluid and the amine solvent in a rich state.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 15/951,432, filed on Apr. 12, 2018, the entirecontents of which are incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to systems and methods that integrate a flaregas recovery process with a gas sweetening process used in oil and gasrefining.

BACKGROUND

Many industrial plants around the world utilize gas flares primarily toburn off waste gas that is released by safety valves. The safety valvescan open during planned events, such as plant startup and shutdown, orduring an unplanned event during processing, for example, to preventover-pressuring in industrial plant equipment. By burning the waste gas,the flare breaks down waste gas into compounds that are moreenvironmentally friendly when released into the atmosphere as well asprevents large volumes of flammable gas to be blown by wind to areasthat can potentially cause safety issues.

In a flare, a continuous flow of waste gas is provided to the gas flareto maintain a constant flame. If the flare tip loses its flame, theflare will fail to burn the waste gas and the waste gas will simplydischarge into the atmosphere. Because the flare discharges combustedgases to the atmosphere, an associated piping system called a flareheader, which routes fluids to the flare, normally operates a littleabove atmospheric pressure. The waste gas that enters the flare headerhas a pressure that is too low to be of practical use in an oil and gasrefining plant.

SUMMARY

This document relates to systems and methods that integrate a flare gasrecovery process with a gas sweetening process used in oil and gasrefining. In particular, this specification describes a system andmethod of utilizing liquid amine solvent from a gas sweetening unit asmotive fluid for an ejector for application in flare gas recovery.

The present disclosure includes one or more of the following units ofmeasure with their corresponding abbreviations, as shown in Table 1:

TABLE 1 Unit of Measure Abbreviation Degrees Fahrenheit ° F. Parts permillion ppm Pounds per square inch (pressure) psi Pounds per square inchgauge (pressure) psig One million MM Standard cubic feet per day SCFDgallons per minute gpm (U.S. measure) Mole mol

Oil refineries and gas processing facilities across the world canproduce large amounts of waste gas. Flare gas recovery systems can beinstalled to recover this waste gas. A flare gas recovery process is aprocess that reutilizes a waste gas as a fuel gas when typically, thewaste gas would be sent to a gas flare for disposal. Recovering wastegas can save operation costs associated with purchased fuel because someor all of the recovered flare gas can be used as fuel. Furthermore,flare gas recovery systems can reduce emissions and increase the life ofthe flare tip. If the recovered flare gas is further processed andcleaned, the flare gas can even be acceptable for venting. Flare gasrecovery systems can include equipment to compress the waste gas so thatthe gas can be recycled back to the plant. However, instead of usingmulti-stage compressors, which are typically associated with highcapital costs due to associated equipment, installation, and highoperation costs, the systems and method described in this document useanother option for compressing flare gas—which is to employ ejectors.

Ejectors rely on a Venturi effect to pressurize flare gas by utilizingavailable pressure from a fluid called a motive fluid. Ejectors areconsidered static equipment and are generally associated with lowcapital and operating costs in comparison to compressors. The ejectorconverts the pressure energy available in the motive fluid to velocityenergy, brings in the low pressure suction fluid, mixes the two fluids,and discharges the mixture at an intermediate pressure without the useof rotating or moving parts.

In some embodiments, a liquid-driven ejector can be integrated with aflare gas recovery system. Such systems are more complicated thansystems that use vapor-driven ejectors because of the need to separatethe liquid and vapor phases downstream of the ejector. The advantage ofa liquid-driven ejector, however, is that the liquid can be pumped andrecycled as motive fluid, resulting in a net discharge of only therecovered flare gas and therefore, having significantly less impact ondownstream units. Water is a viable option for motive fluid, bututilizing water introduces additional issues, such as water treatmentand special materials to handle sour water, corrosion issues, andadditional filtration needs. The integration and utilization ofavailable solvent from the gas sweetening unit therefore provides theadvantages of avoiding the issues associated with water-driven ejectors,while also adding the capability of cleaning the flare gas beforerecycling it back to the facility.

In an example implementation, a flare gas recovery system includes aprimary gas sweetening unit; and a liquid-driven ejector in continuousfluid communication with the primary gas sweetening unit. The ejectorincludes an inlet configured to receive a motive fluid including aregenerable amine solvent in a rich state from the primary gassweetening unit; a gas inlet configured to receive a suction fluidincluding a gas; and a fluid outlet configured to either directly orindirectly discharge to the primary gas sweetening unit a two-phasefluid including a mixture of the suction fluid and the amine solvent ina rich state.

In an aspect combinable with the example implementation, the aminesolvent interacts with one or more components of the suction fluid inthe ejector, the one or more components include hydrogen sulfide, carbondioxide, or both.

In another aspect combinable with any one of the previous aspects, theamine solvent interacts with one or more components of gas by chemicalbinding, physical binding, or both, to produce the amine solvent in therich state from the motive fluid and a gas configured for gas sweeteningfeed, combustion, venting, or flaring from the suction fluid.

Another aspect combinable with any one of the previous aspects furtherincludes a filtration package to remove impurities from the solvent,wherein the impurities include corrosion particles or salts that form inthe system during operation.

Another aspect combinable with any one of the previous aspects furtherincludes a circulation pump to supply flow of the motive fluid from theprimary gas sweetening unit to the ejector.

Another aspect combinable with any one of the previous aspects furtherincludes a separator to separate the two-phase fluid into a rich solventliquid phase and a sweetened gas vapor phase.

Another aspect combinable with any one of the previous aspects furtherincludes a secondary gas sweetening unit operating at a lower pressurethan the primary gas sweetening unit, wherein the rich solvent liquidphase from the separator is cycled back to the primary gas sweeteningunit, and the sweetened gas vapor phase from the separator is deliveredas feed to the secondary gas sweetening unit.

Another aspect combinable with any one of the previous aspects furtherincludes a booster pump to pressurize the motive fluid to the ejector tomeet operating conditions of the secondary gas sweetening unit.

In another aspect combinable with any one of the previous aspects, thesuction fluid includes a flare gas from a source including a main flareheader, upstream of a flashback protection device.

In another aspect combinable with any one of the previous aspects, thesuction fluid includes a flare gas from a source including one or moreof emergency valves in the primary gas sweetening unit or a main flareheader, upstream of a flashback protection device.

In another example implementation, a method of supplying flare gas for aflare gas recovery system includes supplying a flow of flare gas to anejector of the flare gas recovery system; supplying a continuous flow ofregenerable amine solvent in a rich state to the ejector from a primarygas sweetening unit that is in fluid communication with the flare gasrecovery system; and combining the flare gas and solvent together in theejector to form a two-phase fluid, where the continuous flow of thesolvent is configured to increase pressure of the flare gas to allow fordelivery of the two-phase fluid either directly or indirectly back tothe primary gas sweetening unit.

In an aspect combinable with the example implementation, combining ofthe flare gas and solvent causes removal of a portion of one or morecomponents from the gas, the one or more components including hydrogensulfide or carbon dioxide, by chemical binding, physical binding, orboth, thereby resulting in the two-phase fluid including of the solventin a rich state and the gas suitable for one or more of gas sweeteningfeed, combustion, venting, and flaring.

Another aspect combinable with any one of the previous aspects furtherincludes filtering of the solvent to remove impurities, the impuritiesincluding corrosion particles or salts.

In another aspect combinable with any one of the previous aspects,supplying the solvent in rich state is provided by a pressure source,the pressure source including booster pumps designated for the flare gasrecovery system, to meet operating conditions of a secondary gassweetening unit.

In another aspect combinable with any one of the previous aspects,supplying the solvent in rich state is provided by a pressure source,the pressure source including circulation pumps in the primary gassweetening unit or additional circulation pumps designated for the flaregas recovery system.

Another aspect combinable with any one of the previous aspects furtherincludes separating the two-phase fluid into a rich solvent liquid phaseand a sweetened gas vapor phase.

Another aspect combinable with any one of the previous aspects furtherincludes cycling the liquid phase back to the primary gas sweeteningunit, and delivering the vapor phase to a secondary gas sweetening unit.

In another aspect combinable with any one of the previous aspects,supplying the flow of flare gas to the ejector includes supplying gasfrom a main flare header, upstream of a flashback protection device.

In another aspect combinable with any one of the previous aspects,supplying the flow of flare gas to the ejector includes supplying gasfrom one or more of emergency valves in the primary gas sweetening unitor a main flare header, upstream of a flashback protection device.

In another example implementation, a flare gas recovery system includesa primary gas sweetening unit; and a liquid-driven ejector in continuousfluid communication with the primary gas sweetening unit. The ejectorincludes an inlet configured to receive a motive fluid including aregenerable amine solvent in a lean state from the primary gassweetening unit; a gas inlet configured to receive a suction fluidincluding a gas; and a fluid outlet configured to either directly orindirectly discharge to the primary gas sweetening unit a two-phasefluid including a mixture of the suction fluid and the amine solvent ina rich state.

In an aspect combinable with the example implementation, theliquid-driven ejector includes a first liquid-driven ejector.

Another aspect combinable with any one of the previous aspects furtherincludes a second liquid-driven ejector in continuous fluidcommunication with the primary gas sweetening unit.

In another aspect combinable with any one of the previous aspects, thesecond liquid-driven ejector includes an inlet configured to receive amotive fluid including a lean or sour gas stream; a gas inlet configuredto receive a suction fluid including a flare gas; and a fluid outletconfigured to either directly or indirectly discharge to the firstliquid-driven ejector a two-phase fluid including a mixture of thesuction fluid and motive fluid.

In another aspect combinable with any one of the previous aspects, thetwo-phase fluid includes primarily flare gas.

In another aspect combinable with any one of the previous aspects, theamine solvent interacts with one or more components of the suction fluidin the ejector, the one or more components include hydrogen sulfide,carbon dioxide, or both.

In another aspect combinable with any one of the previous aspects, theamine solvent interacts with one or more components of gas by chemicalbinding, physical binding, or both, to produce the amine solvent in therich state from the motive fluid and a gas configured for gas sweeteningfeed, combustion, venting, or flaring from the suction fluid.

Another aspect combinable with any one of the previous aspects furtherincludes a filtration package to remove impurities from the solvent,wherein the impurities include corrosion particles or salts that form inthe system during operation.

Another aspect combinable with any one of the previous aspects furtherincludes a circulation pump to supply flow of the motive fluid from theprimary gas sweetening unit to the ejector; and a separator to separatethe two-phase fluid into a rich solvent liquid phase and a sweetened gasvapor phase.

Another aspect combinable with any one of the previous aspects furtherincludes a secondary gas sweetening unit operating at a lower pressurethan the primary gas sweetening unit, wherein the rich solvent liquidphase from the separator is cycled back to the primary gas sweeteningunit, and the sweetened gas vapor phase from the separator is deliveredas feed to the secondary gas sweetening unit.

Another aspect combinable with any one of the previous aspects furtherincludes a booster pump to provide adequate pressure to the motive fluidto the ejector, to meet operating conditions of the secondary gassweetening unit.

In another aspect combinable with any one of the previous aspects, thesuction fluid includes a flare gas from a source including a main flareheader, upstream of a flashback protection device.

In another aspect combinable with any one of the previous aspects, thesuction fluid includes a flare gas from a source including one or moreof emergency valves in the primary gas sweetening unit or a main flareheader, upstream of a flashback protection device.

In another example implementation, a method of supplying flare gas for aflare gas recovery system includes supplying a flow of flare gas to aflare gas ejector of the flare gas recovery system; supplying acontinuous flow of a lean or sour gas stream to the ejector; combiningthe flare gas and lean or sour gas stream together in the ejector toform a mixed gas fluid, supplying a flow of the mixed-gas fluid to anamine ejector of a gas sweetening unit; supplying a continuous flow ofregenerable amine solvent in a lean state to the amine ejector from theprimary gas sweetening unit that is in fluid communication with theflare gas recovery system; and combining the mixed-gas fluid and solventtogether in the amine ejector to form a two-phase fluid, where thecontinuous flow of the solvent is configured to increase pressure of themixed-gas fluid to allow for delivery of the two-phase fluid eitherdirectly or indirectly back to the primary gas sweetening unit.

In an aspect combinable with the example implementation, combining ofthe mixed-gas fluid and solvent causes removal of a portion of one ormore components from the mixed-gas, the one or more components includinghydrogen sulfide or carbon dioxide, by chemical binding, physicalbinding, or both, thereby resulting in the two-phase fluid including ofthe solvent in a rich state and the gas suitable for one or more of gassweetening feed, combustion, venting, and flaring.

Another aspect combinable with any one of the previous aspects furtherincludes filtering of the solvent to remove impurities, the impuritiesincluding corrosion particles or salts.

In another aspect combinable with any one of the previous aspects,supplying the solvent in lean state is provided by a pressure source,the pressure source including circulation pumps in the primary gassweetening unit or additional circulation pumps designated for the flaregas recovery system.

Another aspect combinable with any one of the previous aspects furtherincludes separating the two-phase fluid into a rich solvent liquid phaseand a sweetened gas vapor phase.

Another aspect combinable with any one of the previous aspects furtherincludes cycling the liquid phase back to the primary gas sweeteningunit, and delivering the vapor phase to a secondary gas sweetening unit.

In another aspect combinable with any one of the previous aspects,supplying the lean solvent is further assisted by an additional pressuresource, the pressure source including booster pumps designated for theflare gas recovery system, to meet operating conditions of the secondarygas sweetening unit.

In another aspect combinable with any one of the previous aspects,supplying the flow of flare gas to the flare gas ejector includessupplying gas from a main flare header, upstream of a flashbackprotection device.

In another aspect combinable with any one of the previous aspects,supplying the flow of flare gas to the flare gas ejector includessupplying gas from one or more of emergency valves in the primary gassweetening unit or a main flare header, upstream of a flashbackprotection device.

The subject matter described in this specification can be implemented inparticular implementations, so as to realize one or more of thefollowing advantages. The integrated processes and systems described inthis document can provide an alternative to using a gas flare system, oranother waste gas disposal system, which allows a gas refinery companyto meet certain quality and regulatory emissions standards. Theintegrated systems and methods described in this document can reducecapital and operating costs by reducing the need for additional powerand equipment, such as a knockout vessel and a cooler, in comparison toexisting systems that recover waste gases. The integrated systems andmethods described in this document can reduce capital and operatingcosts by reducing the need for additional processing, such as cooling orremoving acid gas. The integrated systems and processes described inthis document can require less area in comparison to existing systemsused for disposing waste gases. Although the gas could be treated whenpassing through the ejector and subsequently sent to an end user,certain embodiments of the integrated systems and processes described inthis document recycle waste gas back to the process to reduce netproduction of waste gas. For example, in some embodiments, the gas froman ejector outlet can be routed back to an amine unit in the system. Theintegrated systems and methods described in this document provideadditional capability to clean recovered flare gas by nature of thechosen motive fluid. Other advantages will be apparent to those ofordinary skill in the art.

The details of one or more implementations of the subject matter of thisspecification are set forth in the accompanying drawings and thedescription. Other features, aspects, and advantages of the subjectmatter will become apparent from the description, the drawings, and theclaims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an example system that includes a flaregas recovery unit and two gas sweetening units.

FIG. 2 is a schematic diagram of another example system that integratesa flare gas recovery unit with a gas sweetening unit, where the flaregas is recovered from a main flare header.

FIG. 3 is a schematic diagram of another example system that integratesa flare gas recovery unit with a gas sweetening unit, where the flaregas is recovered from the gas sweetening unit.

FIG. 4 is a schematic diagram of an example system that includes a flaregas recovery unit and a gas sweetening unit.

FIG. 5 is a schematic diagram of another example system that integratesa flare gas recovery unit with a gas sweetening unit, where the flaregas is recovered from a main flare header.

FIG. 6 is a schematic diagram of another example system that integratesa flare gas recovery unit with a gas sweetening unit, where the flaregas is recovered from a main flare header.

DETAILED DESCRIPTION

This document describes systems and methods that integrate a flare gasrecovery unit with a gas sweetening unit, and is presented to enable anyperson skilled in the art to make and use the disclosed subject matterin the context of one or more particular implementations.

After crude oil or natural gas is extracted, it must be refined toproduce commercial fuels and other products. Oil or gas that containssignificant amounts of sulfur compounds like hydrogen sulfide isconsidered “sour,” and oil refineries and gas processing plants utilize“sweetening” processes to remove these sulfur compounds. Gas sweeteningunits typically utilize an aqueous solution of amine solvent to removehydrogen sulfide and carbon dioxide from sour gas.

FIG. 1 depicts a general schematic of a first exemplary system 100 thatincludes a primary gas sweetening unit 110 and flare gas recovery system130. The primary gas sweetening unit 110 of FIG. 1 comprises an aminecontactor 112, a flash drum 114, an amine stripper 118, an aminecirculation pump 120, and an amine cooler 122. The amine contactor 112is a counter-flow gas-liquid contactor that can be referred as anabsorber, treater, or scrubber. The amine contactor 112 is a vesselcomprising internal components, which can include trays or packing, toincrease gas-liquid contact.

The flash drum 114 operates at a lower pressure than the contactor 112and allows light hydrocarbons to flash (that is, evaporate) from theamine solvent. The flash drum 114 is sized for liquid surge, liquidholdup, and residence time for vapor to separate from the liquid aminesolvent. In some embodiments, the flash drum 114 is equipped with atower 116. The flash drum tower 116 can remove acid gas such as hydrogensulfide, which can be present in the vapor separated from the aminesolvent, before the vapor is sent to another downstream process or enduser.

Still referring to FIG. 1 , the amine stripper 118 is a vessel, whichcan also be referred to as a regenerator. The amine stripper 118comprises internal components, for example, trays or packing, andeffectively serves as a distillation tower to boil off acid gas toregenerate the amine solvent. The distinction between acid gas and sourgas is that sour gas is mostly hydrocarbons with some acidic gascontent, and acid gas contains little to no hydrocarbons.

The circulation pump 120 pressurizes the regenerated amine solvent torecycle the amine solvent back to the contactor 112. The circulationpump 120 can comprise a single pump or multiple pumps in parallel or inseries. The circulation pump 120 can be sized to accommodate upsetscenarios which require much higher flow rates than is normally requiredby the primary gas sweetening unit 110. The circulation pump 120, asdepicted in FIG. 1 , employs a recycle line which routes a portion ofthe amine solvent back to the suction of the pump 120.

The amine cooler 122 brings the temperature of the solvent down beforethe solvent is recycled back to the contactor 112. The lower solventtemperature increases the efficiency of cleaning the sour gas thatenters the contactor 112. The cooler 122 can be a shell-and-tube heatexchanger, an air cooler, or a combination of multiples of both.

Gas sweetening units can optionally comprise auxiliary and variantequipment such as additional heat exchangers and vessels that have notbeen described above, but a majority of gas sweetening units across theworld implement some variation or combination of the major equipmentoutlined.

Gas sweetening units can operate at a variety of operating temperaturesand pressures. In some embodiments, sour gas at a temperature of between70-130° F. via stream 111 enters the bottom of an amine contactor 112,as amine solvent at a temperature of between 80-140° F. via stream 113enters from the top. The amine solvent that enters the amine contactor112 is at least approximately 10° F. hotter than the sour gas thatenters the amine contactor 112. As the amine solvent contacts the sourgas, the solvent removes (or “cleans”) the sulfur compounds, carbondioxide, and other contaminants from the sour gas, by chemical andphysical binding. Once the solvent has passed through contactor 112, thesolvent is considered to be in a “rich” state—also referred as “richsolvent”-because the solvent contains the hydrogen sulfide removed fromthe sour gas. The sweetened gas exits from the top of contactor 112 viastream 129, and rich solvent exits from the bottom via stream 115. Thesweetened gas (stream 129) can contain approximately 5-60 ppm hydrogensulfide and is sent downstream for sale or further processing. Richsolvent 115 is sent to a flash drum 114 operating between atmosphericpressure to 90 psig, where any flashed vapor travels up a flash drumtower 116 and exits via stream 119, where the flashed vapor can then beutilized as fuel, vented, flared, or a combination of these.

Rich solvent liquid 117 from flash drum 114 is sent to an amine stripper118 with a top operating pressure between 5-17 psig. The hydrogensulfide and carbon dioxide is boiled off via heat input to the bottom ofstripper 118 operating between 230-270° F. in order to regenerate theamine solvent. The regenerated solvent is then considered to be in a“lean” state—also referred as “lean solvent”—that is once again suitableto be used for cleaning additional sour gas. Sour gas 123, comprisinghydrogen sulfide and carbon dioxide exits the top of stripper 118, andlean solvent 121 is pumped out of the bottom of stripper 118 bycirculation pump 120. Lean solvent 127 is cooled in heat exchanger 112to approximately 80-140° F. before re-entering contactor 112 to be usedagain to clean additional sour gas. The transport of vapor and liquidwithin, to, and from the gas sweetening unit 110 can be achieved usingvarious piping, pump, and valve configurations.

Still referring to FIG. 1 , the exemplary system 100 includes the flaregas recovery system 130 that is integrated with the gas sweetening unit110, as described above. The system 100 utilizes liquid amine solvent125 from the gas sweetening unit 110 as motive fluid for an ejector inthe flare gas recovery system 130.

The flare gas recovery system 130 includes an ejector 134 that comprisesan inlet that continuously receives the regenerable amine solvent, whichserves as a high-pressure motive fluid from the gas sweetening unit 110via stream 125. The ejector 134 also comprises a gas inlet configuredfor receiving a flare gas 133 as a low-pressure suction fluid. Themotive fluid operates at a higher pressure than the suction fluid. Forexample, the amine solvent (motive fluid) operates at approximately 990psig, and the flare gas (suction fluid) operates at approximately 0.5psig. The motive and suction fluid mix within the ejector 134, and thendischarge at an intermediate pressure. Because the motive fluid is aminesolvent 125 from the gas sweetening unit 110, the motive fluid iscapable of removing hydrogen sulfide and carbon dioxide from the flaregas.

FIG. 1 shows a certain implementation in which the suction gas of theejector 134 is supplied by a flare header 131 via stream 133. System 100can include a secondary gas sweetening unit 150 (including a secondaryamine contactor 152), which operates at a lower pressure than theprimary gas sweetening unit 110. The ejector 134 can be installed nearthe flare header 131 and utilize amine solvent from a nearby gassweetening unit, such as the primary gas sweetening unit 110, as motivefluid to mix with and pressurize flare gas. The two-phase mixture 137can be discharged to a separator 136, where vapor phase 143 is separatedfrom liquid phase 141 of the mixture. The liquid phase includes richsolvent and can be recycled back to the primary gas sweetening unit 110and returned to a flash drum 114 via stream 141. The vapor phase 143includes sweetened gas and can be delivered as additional feed (forexample, in addition to the feed 151 to the secondary amine contactor152) to the secondary gas sweetening unit 150. The type of system shownin FIG. 1 can be applicable when there exists at least two gassweetening units operating at different pressures. In someimplementations, a booster pump is included to provide adequate pressureto the amine solvent from the primary gas sweetening unit 110 which isbeing utilized as motive fluid for the ejector 134, so that therecovered flare gas can be sent to the secondary gas sweetening unit150.

The flare gas recovery system 130 design takes into consideration theintegrated operation with the flare 170, which includes flashbackprevention 132. Flashback prevention involves preventing reverse flow ofgas and potentially, the flame from the flare, as flare gas 135 is beingburned at the flare 170. Flashback prevention can comprise a liquid sealdrum, a molecular seal, a fluidic seal, a flame arrestor, or anycombination thereof. The source of flare gas to the ejector 134 (oranalogous 234, 334) is upstream of the flashback prevention 132.

FIG. 2 provides a general schematic of a second exemplary system 200that includes a gas sweetening unit 210 and flare gas recovery system230. As depicted in FIG. 2 , the sweetening unit 210 is substantiallythe same as the sweetening unit 110 of FIG. 1 , but the configuration ofthe flare gas recovery system 230 differs from the flare gas recoverysystem 130 of FIG. 1 . Like element numbers across the figures can besubstantially the same; for example, the amine contactors 212 and 312can be substantially the same as the amine contactor 112. The ejector234 can be installed near the flare header 231 and utilize amine solvent225 from a nearby gas sweetening unit, such as the primary gassweetening unit 210, as motive fluid to mix with and pressurize flaregas 233. The two-phase mixture from the ejector 234 can be recycled backto the primary gas sweetening unit 210 and discharged directly back to aflash drum 214 via stream 239. The vapor phase can be separated fromliquid phase in the flash drum 214 because the both the liquid and gasfrom the ejector 234 are recycled back to the gas sweetening unit 210.Because flare gas is being recovered and recycled to the gas sweeteningunit 210, downstream units can require modification to accommodate theincreased vapor flow—for example, flash drum tower 216. The recoveredflare gas can then be utilized as fuel, vented, flared, or a combinationof these.

FIG. 3 provides a general schematic of a third exemplary system 300 thatincludes a gas sweetening unit 310 and flare gas recovery system 330. Asdepicted in FIG. 3 , the sweetening unit 310 is substantially the sameas the sweetening unit 110 of FIG. 1 , but the configuration of theflare gas recovery system 330 differs from the flare gas recovery system130 of FIG. 1 . The ejector 334 can be installed near a gas sweeteningunit, such as the gas sweetening unit 310, and utilize amine solvent 325from the gas sweetening unit 310 as motive fluid to mix with andpressurize waste gas 343 from the gas sweetening unit 310. The two-phasemixture from the ejector 334 can be recycled back to the gas sweeteningunit 310 and discharged directly back to a flash drum 314 via stream339. For example, FIG. 3 shows a certain implementation in which thesuction gas of the ejector 334 is supplied by emergency valves from thegas sweetening unit 310 via stream 341. Some or all of the losses fromthe unit can immediately be recovered before reaching a flare header331. Although the configuration is different, the source of flare gas tothe ejector 334 is still upstream of the flashback prevention 332.

In some implementations, an additional circulation pump is included toprovide adequate flow of amine solvent from the primary gas sweeteningunit 110 (or analogous 210, 310) which is being utilized as motive fluidfor the ejector 134 (or analogous 234, 334).

Referring to the exemplary system 100 in FIG. 1 , in one example of thesystems described in this document, the amine contactor 112 of theprimary gas sweetening unit 110 can operate at approximately 980 psig.The lean amine solvent from the amine cooler 122 can enter the contactor112 at approximately 140° F., and the sweet gas (stream 129) exits thecontactor 112 at approximately 120° F. The flash drum 114 can operate atapproximately 80 psig and receives liquid from the bottom of thecontactor 112 and the bottom of the separator 136 from the flare gasrecovery system 130. The flashed vapor can travel up the flash drumtower 116 and be sent to boilers, where the gas is burned to provideheat for another process. The liquid from the flash drum 114 can be sentto the amine stripper 118 with a bottom operating pressure ofapproximately 15 psig and a bottom operating temperature ofapproximately 265° F. The circulation pump 120 can normally circulate atapproximately 9500 gpm with a discharge pressure of approximately 990psig. Approximately 7000 gpm of the amine solvent can be circulated backto the contactor 112 through cooler 122, 1200 gpm can be sent to theejector 134 of the flare gas recovery system 130, and the balance can berecycled back to the suction of circulation pump 120.

In some embodiments, a portion of the flare gas from the flare header131 can be sent to the ejector 134, upstream of the seal drum 132, whichis utilized for flashback prevention and liquid knockout. The aminesolvent and flare gas can be mixed within ejector 134 and discharged atapproximately 210 psig. The vapor-liquid mixture 137 can be sent toseparator 136, where the liquid 141 at the bottom is sent back to theprimary gas sweetening unit 110, and the vapor 143 at the top is sent asadditional feed to the secondary gas sweetening unit 150, which operatesat approximately 180 psig.

The approximate flow rates and compositions of the streams can be:

Stream Number* units 111 113 119 121 123 125 129 131 137 143 Vapor flowMMSCFD 600 — 0.9 — 63 — 535 2 2 2 Liquid flow gpm — 7000 — 8200 — 1200 —— 1200 — Vapor composition mol % ** ** methane 70.0 — 91.0 — — — 78.485.5 90.5 — ethane 6.0 — 5.0 — — — 6.7 2.0 2.1 — propane 2.5 — — — — —2.8 — — — i-butane 0.5 — — — — — 0.6 — — — n-butane 0.4 — — — — — 0.4 —— — i-pentane 0.4 — — — — — 0.4 — — — n-pentane 0.3 — — — — — 0.3 — — —carbon dioxide 5.0 — — — 48.0 — — 2.5 — — hydrogen sulfide 5.5 — — —52.0 — — 3.0 — — nitrogen 9.4 — 4.0 — — — 10.5 7.0 7.4 — water 0.1 — — —— — — — — — *Refer to FIG. 1. **Composition is in dry basis.

Referring to the exemplary system 200 in FIG. 2 , in one example of thesystems described in this document, the amine contactor 212 of the gassweetening unit 210 can operate at approximately 980 psig. The leanamine solvent from the amine cooler 222 can enter the contactor 212 atapproximately 140° F., and the sweet gas (stream 229) can exit thecontactor 212 at approximately 120° F. The flash drum 214 can operate atapproximately 80 psig and receive liquid from the bottom of thecontactor 212 and a vapor-liquid mixture from the ejector 234 from theflare gas recovery system 230. The flashed vapor can travel up the flashdrum tower 216 and be sent to boilers, where the gas is burned toprovide heat for another process. The liquid from the flash drum 214 canbe sent to the amine stripper 218 with a bottom operating pressure ofapproximately 15 psig and a bottom operating temperature ofapproximately 265° F. The circulation pump 220 can normally circulate atapproximately 9500 gpm with a discharge pressure of approximately 990psig. Approximately 7000 gpm of the amine solvent can be circulated backto the contactor 212 through cooler 222 such that 1200 gpm is sent tothe ejector 234 of the flare gas recovery system 230 and the balance isrecycled back to the suction of circulation pump 220.

In some embodiments, portion of the flare gas from the flare header 231can be sent to the ejector 234, upstream of the seal drum 232 forflashback prevention and liquid knockout. The amine solvent and flaregas can be mixed within ejector 234 and discharged a s avapor-liquidmixture back to the flash drum 214 of the gas sweetening unit 210.

The approximate flow rates and compositions of the streams can be:

Stream Number* units 211 213 219 221 223 225 229 231 Vapor flow MMSCFD600 — 2.79 — 63 — 535 2 Liquid flow gpm — 7000 — 8200 — 1200 — — Vaporcomposition mol % ** ** methane 70.0 — 90.6 — — — 78.4 85.5 ethane 6.0 —3.1 — — — 6.7 2.0 propane 2.5 — 0.0 — — — 2.8 — i-butane 0.5 — — — — —0.6 — n-butane 0.4 — — — — — 0.4 — i-pentane 0.4 — — — — — 0.4 —n-pentane 0.3 — — — — — 0.3 — carbon dioxide 5.0 — — — 48.0 — — 2.5hydrogen sulfide 5.5 — — — 52.0 — — 3.0 nitrogen 9.4 — 6.3 — — — 10.57.0 water 0.1 — — — — — — — *Refer to FIG. 2. **Composition is in drybasis.

Referring to the exemplary system 300 in FIG. 3 , in one example of thesystems described in this document, the amine contactor 312 of the gassweetening unit 310 can operate at approximately 980 psig. The leanamine solvent from the amine cooler 322 can enter the contactor 312 atapproximately 140° F., and the sweet gas (stream 329) can exit thecontactor 312 at approximately 120° F. The flash drum 314 can operate atapproximately 80 psig and receive liquid from the bottom of thecontactor 312 and a vapor-liquid mixture from the ejector 334 from theflare gas recovery system 330. The flashed vapor can travel up the flashdrum tower 316 and be sent to boilers, where the gas is burned toprovide heat for another process. The liquid from the flash drum 314 canbe sent to the amine stripper 318 with a bottom operating pressure ofapproximately 15 psig and a bottom operating temperature ofapproximately 265° F. The circulation pump 320 can normally circulateapproximately 9500 gpm with discharge pressure of approximately 990psig. Approximately 7000 gpm of the amine solvent can be circulated backto the contactor 312 through cooler 322 such that 190 gpm is sent to theejector 334 of the flare gas recovery system 330, and the balance isrecycled back to the suction of circulation pump 320.

Some of the flare gas from the flare header 331 is sent to the ejector334, upstream of the seal drum 332, which is utilized for flashbackprevention and liquid knockout. The ejector 334 is also lined up toreceive flare gas directly from the gas sweetening unit 310, by stream341 which is an emergency valve discharge header for the gas sweeteningunit 310. In some cases, an emergency valve in the gas sweetening unit310 can be opened and the gas can be recovered before being sent to theflare header 331. The amine solvent and flare gas can be mixed withinejector 334 and discharged as a vapor-liquid mixture back to the flashdrum 314 of the gas sweetening unit 310.

The approximate flow rates and compositions of the streams can be:

Stream Number* units 311 313 319 321 323 325 329 341 Vapor flow MMSCFD600 — 1.25 — 63 — 535 0.35 Liquid flow gpm — 7000 — 8200 — 190 — — Vaporcomposition mol % ** ** methane 70.0 — 88.6 — — — 78.4 56.6 ethane 6.0 —5.4 — — — 6.7 4.9 propane 2.5 — 0.6 — — — 2.8 2.0 i-butane 0.5 — — — — —0.6 — n-butane 0.4 — — — — — 0.4 — i-pentane 0.4 — — — — — 0.4 —n-pentane 0.3 — — — — — 0.3 — carbon dioxide 5.0 — — — 48.0 — — 13.9hydrogen sulfide 5.5 — — — 52.0 — — 15.1 nitrogen 9.4 — 5.4 — — — 10.57.6 water 0.1 — — — — — — — *Refer to FIG. 3. **Composition is in drybasis.

In some implementations, a filtration package can be included to removeimpurities like salts or corroded materials that accumulate in thesolvent used for the gas sweetening process. The filtration package cancomprise a filter housing, a filter element or cartridge, an additionalcirculation pump, or a combination of multiples of these. Impuritiescollect on the filter element or cartridge as a fluid passes through thefilter. The filter element or cartridge can be cleaned or replacedperiodically.

FIG. 4 depicts a general schematic of a fourth exemplary system 400 thatincludes a primary gas sweetening unit 410 and flare gas recovery system430. The primary gas sweetening unit 410 of FIG. 4 comprises an aminecontactor 412, a flash drum 414, an amine stripper 418, an aminecirculation pump 420, and an amine cooler 422. The amine contactor 412is a counter-flow gas-liquid contactor that can be referred as anabsorber, treater, or scrubber. The amine contactor 412 is a vesselcomprising internal components, which can include trays or packing, toincrease gas-liquid contact.

The flash drum 414 operates at a lower pressure than the contactor 412and allows light hydrocarbons to flash (that is, evaporate) from theamine solvent. The flash drum 414 is sized for liquid surge, liquidholdup, and residence time for vapor to separate from the liquid aminesolvent. In some embodiments, the flash drum 414 is equipped with atower 416. The flash drum tower 416 can remove acid gas such as hydrogensulfide, which can be present in the vapor separated from the aminesolvent, before the vapor is sent to another downstream process or enduser.

Still referring to FIG. 4 , the amine stripper 418 is a vessel, whichcan also be referred to as a regenerator. The amine stripper 418comprises internal components, for example, trays or packing, andeffectively serves as a distillation tower to boil off acid gas toregenerate the amine solvent. The distinction between acid gas and sourgas is that sour gas is mostly hydrocarbons with some acidic gascontent, and acid gas contains little to no hydrocarbons.

The circulation pump 420 pressurizes the regenerated amine solvent torecycle the amine solvent back to the contactor 412. The circulationpump 420 can comprise a single pump or multiple pumps in parallel or inseries. The circulation pump 420 can be sized to accommodate upsetscenarios which require much higher flow rates than is normally requiredby the primary gas sweetening unit 410. The circulation pump 420, insome aspects, can employ a recycle line which routes a portion of theamine solvent back to the suction of the pump 420. Further, a boosterpump (or pumps) may be positioned to pressurize the rich amine solvent415 to the ejector 434.

The amine cooler 422 brings the temperature of the solvent down beforethe solvent is recycled back to the contactor 412. The lower solventtemperature increases the efficiency of cleaning the sour gas thatenters the contactor 412. The cooler 422 can be a shell-and-tube heatexchanger, an air cooler, or a combination of multiples of both.

Gas sweetening units can optionally comprise auxiliary and variantequipment such as additional heat exchangers and vessels that have notbeen described above, but a majority of gas sweetening units across theworld implement some variation or combination of the major equipmentoutlined.

Gas sweetening units can operate at a variety of operating temperaturesand pressures. In some embodiments, sour gas at a temperature of between70-130° F. via stream 411 enters the bottom of an amine contactor 412,as amine solvent at a temperature of between 80-140° F. via stream 413enters from the top. The amine solvent that enters the amine contactor412 is at least approximately 10° F. hotter than the sour gas thatenters the amine contactor 412. As the amine solvent contacts the sourgas, the solvent removes (or “cleans”) the sulfur compounds, carbondioxide, and other contaminants from the sour gas, by chemical andphysical binding. Once the solvent has passed through contactor 412, thesolvent is considered to be in a “rich” state—also referred as “richsolvent”-because the solvent contains the hydrogen sulfide removed fromthe sour gas. The sweetened gas exits from the top of contactor 412 viastream 429, and rich solvent exits from the bottom via stream 415. Thesweetened gas (stream 429) can contain approximately 5-60 ppm hydrogensulfide and is sent downstream for sale or further processing.

As shown, in this example implementation, rich solvent 415 can be sentto an ejector 434 and used as a motive fluid (discussed later) for theejector 434 prior to (or in place of) being sent to a flash drum 414operating between atmospheric pressure to 90 psig, where any flashedvapor travels up a flash drum tower 416 and exits via stream 419, wherethe flashed vapor can then be utilized as fuel, vented, flared, or acombination of these.

Rich solvent liquid 417 from flash drum 414 is sent to an amine stripper418 with a top operating pressure between 5-17 psig. The hydrogensulfide and carbon dioxide is boiled off via heat input to the bottom ofstripper 418 operating between 230-270° F. in order to regenerate theamine solvent. The regenerated solvent is then considered to be in a“lean” state—also referred as “lean solvent”—that is once again suitableto be used for cleaning additional sour gas. Sour gas 423, comprisinghydrogen sulfide and carbon dioxide exits the top of stripper 418, andlean solvent 421 is pumped out of the bottom of stripper 418 bycirculation pump 420. Lean solvent 427 is cooled in heat exchanger 412to approximately 80-140° F. before re-entering contactor 412 to be usedagain to clean additional sour gas. The transport of vapor and liquidwithin, to, and from the gas sweetening unit 410 can be achieved usingvarious piping, pump, and valve configurations.

Still referring to FIG. 4 , the exemplary system 400 includes the flaregas recovery system 430 that is integrated with the gas sweetening unit410, as described above. The system 400 utilizes liquid rich aminesolvent 415 from the gas sweetening unit 410 (for example, circulatedfrom the bottom of the contactor 412) as motive fluid for the ejector434 in the flare gas recovery system 430.

The flare gas recovery system 430 includes the ejector 434 thatcomprises an inlet that continuously receives the rich amine solvent415, which serves as a high-pressure motive fluid from the gassweetening unit 410 via stream 415. The ejector 434 also comprises a gasinlet configured for receiving a flare gas 433 as a low-pressure suctionfluid. The motive fluid operates at a higher pressure than the suctionfluid. For example, the rich amine solvent (motive fluid) operates atapproximately 990 psig, and the flare gas (suction fluid) operates atapproximately 0.5 psig. The motive and suction fluid mix within theejector 434, and then discharge at an intermediate pressure. Because themotive fluid is rich amine solvent 415 from the gas sweetening unit 410,the motive fluid is capable of removing hydrogen sulfide and carbondioxide from the flare gas.

FIG. 4 shows a certain implementation in which the suction gas of theejector 434 is supplied by a flare header 431 via stream 433. In someaspects, system 400 can include a secondary gas sweetening unit (notshown, but similar to unit 150 in FIG. 1 , which includes a secondaryamine contactor 152), which operates at a lower pressure than theprimary gas sweetening unit 410. The ejector 434 can be installed nearthe flare header 431 and utilize rich amine solvent from a nearby gassweetening unit, such as the primary gas sweetening unit 410, as motivefluid to mix with and pressurize flare gas. The two-phase mixture 437can be discharged back to the flash drum 414, where the flashed vaporphase 419 is separated from the rich liquid phase 417 of the mixture. Asshown in this example, a pressure reducing device 439, such as a valveor orifice, is positioned in the conduit for stream 415 between thetake-off to, and the return from, the liquid-driven ejector 434. In someaspects, the pressure reducing device 439 may equalize (or helpequalize) the pressure of the rich solvent 415 and the two-phase mixture437 from the ejector 434 returning to the flash drum 414.

In some aspects, the type of system shown in FIG. 4 can be applicablewhen there exists at least two gas sweetening units operating atdifferent pressures. In some implementations, a booster pump is includedto provide adequate pressure to the rich amine solvent from the primarygas sweetening unit 410 which is being utilized as motive fluid for theejector 434, so that the recovered flare gas can be sent to a secondarygas sweetening unit.

The flare gas recovery system 430 design takes into consideration theintegrated operation with the flare 470, which includes flashbackprevention 432. Flashback prevention involves preventing reverse flow ofgas and potentially, the flame from the flare, as flare gas 435 is beingburned at the flare 470. Flashback prevention can comprise a liquid sealdrum, a molecular seal, a fluidic seal, a flame arrestor, or anycombination thereof. The source of flare gas to the ejector 434 (oranalogous 234, 334) is upstream of the flashback prevention 432.

Referring to the exemplary system 400 in FIG. 4 , in one example of thesystems described in this document, the amine contactor 412 of theprimary gas sweetening unit 410 can operate at approximately 980 psig.The lean amine solvent from the amine cooler 422 can enter the contactor412 at approximately 140° F., and the sweet gas (stream 429) exits thecontactor 412 at approximately 120° F. The flash drum 414 can operate atapproximately 80 psig and receives liquid from the bottom of thecontactor 412 and the bottom of the separator 436 from the flare gasrecovery system 430. The flashed vapor can travel up the flash drumtower 416 and be sent to boilers, where the gas is burned to provideheat for another process. The liquid from the flash drum 414 can be sentto the amine stripper 418 with a bottom operating pressure ofapproximately 15 psig and a bottom operating temperature ofapproximately 265° F. The circulation pump 420 can normally circulate atapproximately 9500 gpm with a discharge pressure of approximately 990psig. Approximately 7000 gpm of the amine solvent can be circulated backto the contactor 412 through cooler 422, 1200 gpm can be sent to theejector 434 of the flare gas recovery system 430, and the balance can berecycled back to the suction of circulation pump 420.

In some embodiments, a portion of the flare gas from the flare header431 can be sent to the ejector 434, upstream of the seal drum 432, whichis utilized for flashback prevention and liquid knockout. The rich aminesolvent and flare gas can be mixed within ejector 434 and discharged atapproximately 210 psig. The vapor-liquid mixture 437 can be sent toseparator 436, where the liquid 441 at the bottom is sent back to theprimary gas sweetening unit 410, and the vapor 443 at the top can besent as additional feed to a secondary gas sweetening unit, which canoperate at approximately 180 psig.

The approximate flow rates and compositions of the streams can be:

Stream Number* units 411 413 419 421 423 425 429 431 437 443 Vapor flowMMSCFD 600 — 0.9 — 63 — 535 2 2 2 Liquid flow gpm — 7000 — 8200 — 1200 —— 1200 — Vapor composition mol % ** ** methane 70.0 — 91.0 — — — 78.585.0 90.5 — ethane 6.0 — 5.0 — — — 6.7 2.0 2.1 — propane 2.5 — — — — —2.8 — — — i-butane 0.5 — — — — — 0.6 — — — n-butane 0.4 — — — — — 0.4 —— — i-pentane 0.4 — — — — — 0.4 — — — n-pentane 0.3 — — — — — 0.3 — — —carbon dioxide 5.0 — — — 48.0 — — 2.5 — — hydrogen sulfide 5.5 — — —52.0 — — 3.0 — — nitrogen 9.4 — 4.0 — — — 10.5 7.0 7.4 — water 0.1 — — —— — — 1.0 — — *Refer to FIG. 4. **Composition is in dry basis.

FIG. 5 depicts a general schematic of a fifth exemplary system 500 thatincludes a primary gas sweetening unit 510 and flare gas recovery system530. The primary gas sweetening unit 510 of FIG. 5 comprises an aminecontactor 512, a flash drum 514, an amine stripper 518, an aminecirculation pump 520, an amine cooler 522, and an amine ejector 534. Theamine contactor 512 is a counter-flow gas-liquid contactor that can bereferred as an absorber, treater, or scrubber. The amine contactor 512is a vessel comprising internal components, which can include trays orpacking, to increase gas-liquid contact.

The flash drum 514 operates at a lower pressure than the contactor 512and allows light hydrocarbons to flash (that is, evaporate) from theamine solvent. The flash drum 514 is sized for liquid surge, liquidholdup, and residence time for vapor to separate from the liquid aminesolvent. In some embodiments, the flash drum 514 is equipped with atower 516. The flash drum tower 516 can remove acid gas such as hydrogensulfide, which can be present in the vapor separated from the aminesolvent, before the vapor is sent to another downstream process or enduser.

Still referring to FIG. 5 , the amine stripper 518 is a vessel, whichcan also be referred to as a regenerator. The amine stripper 518comprises internal components, for example, trays or packing, andeffectively serves as a distillation tower to boil off acid gas toregenerate the amine solvent. The distinction between acid gas and sourgas is that sour gas is mostly hydrocarbons with some acidic gascontent, and acid gas contains little to no hydrocarbons.

The circulation pump 520 pressurizes the regenerated amine solvent torecycle the amine solvent back to the contactor 512. The circulationpump 520 can comprise a single pump or multiple pumps in parallel or inseries. The circulation pump 520 can be sized to accommodate upsetscenarios which require much higher flow rates than is normally requiredby the primary gas sweetening unit 510. The circulation pump 520, insome aspects, can employ a recycle line which routes a portion of theamine solvent back to the suction of the pump 520.

The amine cooler 522 brings the temperature of the solvent down beforethe solvent is recycled back to the contactor 512. The lower solventtemperature increases the efficiency of cleaning the sour gas thatenters the contactor 512. The cooler 522 can be a shell-and-tube heatexchanger, an air cooler, or a combination of multiples of both.

Gas sweetening units can optionally comprise auxiliary and variantequipment such as additional heat exchangers and vessels that have notbeen described above, but a majority of gas sweetening units across theworld implement some variation or combination of the major equipmentoutlined.

Gas sweetening units can operate at a variety of operating temperaturesand pressures. In some embodiments, sour gas at a temperature of between70-130° F. via stream 511 enters the bottom of an amine contactor 512,as amine solvent at a temperature of between 80-140° F. via stream 513enters from the top. The amine solvent that enters the amine contactor512 is at least approximately 10° F. hotter than the sour gas thatenters the amine contactor 512. As the amine solvent contacts the sourgas, the solvent removes (or “cleans”) the sulfur compounds, carbondioxide, and other contaminants from the sour gas, by chemical andphysical binding. Once the solvent has passed through contactor 512, thesolvent is considered to be in a “rich” state—also referred as “richsolvent”-because the solvent contains the hydrogen sulfide removed fromthe sour gas. The sweetened gas exits from the top of contactor 512 viastream 529, and rich solvent exits from the bottom via stream 515. Thesweetened gas (stream 529) can contain approximately 5-60 ppm hydrogensulfide and is sent downstream for sale or further processing. Richsolvent 515 is sent to a flash drum 514 operating between atmosphericpressure to 90 psig, where any flashed vapor travels up a flash drumtower 516 and exits via stream 519, where the flashed vapor can then beutilized as fuel, vented, flared, or a combination of these.

Rich solvent liquid 517 from flash drum 514 is sent to an amine stripper518 with a top operating pressure between 5-17 psig. The hydrogensulfide and carbon dioxide is boiled off via heat input to the bottom ofstripper 518 operating between 230-270° F. in order to regenerate theamine solvent. The regenerated solvent is then considered to be in a“lean” state—also referred as “lean solvent”—that is once again suitableto be used for cleaning additional sour gas. Sour gas 523, comprisinghydrogen sulfide and carbon dioxide exits the top of stripper 518, andlean solvent 521 is pumped out of the bottom of stripper 518 bycirculation pump 520. Lean solvent 527 is cooled in heat exchanger 512to approximately 80-140° F. before re-entering contactor 512 to be usedagain to clean additional sour gas. The transport of vapor and liquidwithin, to, and from the gas sweetening unit 510 can be achieved usingvarious piping, pump, and valve configurations.

Still referring to FIG. 5 , the exemplary system 500 includes the flaregas recovery system 530 that is integrated with the gas sweetening unit510, as described above. The system 500 utilizes liquid amine solvent525 from the gas sweetening unit 510 as motive fluid for the amineejector 534 in the flare gas recovery system 530. The amine ejector 534is positioned, in this example, within the gas sweetening unit 510.

As illustrated in FIG. 5 , a flare gas ejector 540 is also included inthe flare gas system 530 and comprises an inlet that continuouslyreceives a lean or sour gas stream 542 (“gas stream 542”), which servesas a high-pressure motive fluid. The gas ejector 540 also comprises agas inlet configured for receiving a flare gas 533 as a low-pressuresuction fluid. The motive fluid operates at a higher pressure than thesuction fluid. For example, the gas stream 542 (motive fluid) operatesat approximately 990 psig, and the flare gas (suction fluid) operates atapproximately 0.5 psig. The motive and suction fluid mix within theflare gas ejector 534, and then discharge at an intermediate pressure tothe suction of the amine ejector 534 as flare gas stream 541.

FIG. 5 shows a certain implementation in which the discharge of theflare gas ejector 540 is supplied to the suction of the amine ejector534. The amine ejector 534 comprises an inlet that continuously receivesliquid amine solvent 525 from the gas sweetening unit 510, which servesas a high-pressure motive fluid. The motive fluid operates at a higherpressure than the suction fluid (flare gas stream 541). For example, thelean amine liquid solvent 525 (motive fluid) operates at approximately990 psig, and the flare gas stream 541 (suction fluid) operates atapproximately 5-10 psig. The motive and suction fluid mix within theamine ejector 534, and then discharge at an intermediate pressure to theflash drum 514.

The type of system shown in FIG. 5 can also be applicable when thereexists at least two gas sweetening units operating at differentpressures. In some implementations, a booster pump is included toprovide adequate pressure to the amine solvent from the primary gassweetening unit 510 which is being utilized as motive fluid for theamine ejector 534, so that the recovered flare gas can be sent to asecondary gas sweetening unit.

System 500 can include a secondary gas sweetening unit (not shown, butsimilar to unit 150 in FIG. 1 , which includes a secondary aminecontactor 152), which operates at a lower pressure than the primary gassweetening unit 510. The amine ejector 534 can be installed near theflare header 531 and utilize lean amine solvent from a nearby gassweetening unit, such as the primary gas sweetening unit 510, as motivefluid to mix with and pressurize flare gas.

The flare gas recovery system 530 design takes into consideration theintegrated operation with the flare 570, which includes flashbackprevention 532. Flashback prevention involves preventing reverse flow ofgas and potentially, the flame from the flare, as flare gas 535 is beingburned at the flare 570. Flashback prevention can comprise a liquid sealdrum, a molecular seal, a fluidic seal, a flame arrestor, or anycombination thereof. The source of flare gas to the ejector 534 (oranalogous 234, 334) is upstream of the flashback prevention 532.

FIG. 5 provides a general schematic of a fifth exemplary system 500 thatincludes a gas sweetening unit 510 and flare gas recovery system 530. Asdepicted in FIG. 5 , the sweetening unit 510 is substantially the sameas the sweetening unit 110 of FIG. 1 , but the configuration of theflare gas recovery system 530 differs from the flare gas recovery system130 of FIG. 1 . Like element numbers across the figures can besubstantially the same; for example, the amine contactor 512 can besubstantially the same as the amine contactor 112. The amine ejector 534can be installed near the flare header 531 and utilize amine solvent 525from a nearby gas sweetening unit, such as the primary gas sweeteningunit 510, as motive fluid to mix with and pressurize flare gas 533. Thetwo-phase mixture from the ejector 534 can be recycled back to theprimary gas sweetening unit 510 and discharged directly back to a flashdrum 514 via stream 537. The vapor phase can be separated from liquidphase in the flash drum 514, because the both the liquid and gas fromthe ejector 534 are recycled back to the gas sweetening unit 510.Because flare gas is being recovered and recycled to the gas sweeteningunit 510, downstream units can require modification to accommodate theincreased vapor flow—for example, flash drum tower 516. The recoveredflare gas can then be utilized as fuel, vented, flared, or a combinationof these.

In some implementations, an additional circulation pump is included toprovide adequate flow of amine solvent from the gas sweetening unit 510,which is being utilized as motive fluid for the ejector 534.

Referring to the exemplary system 500 in FIG. 5 , in one example of thesystems described in this document, the amine contactor 512 of the gassweetening unit 510 can operate at approximately 980 psig. The leanamine solvent from the amine cooler 522 can enter the contactor 512 atapproximately 140° F., and the sweet gas (stream 529) can exit thecontactor 512 at approximately 120° F. The flash drum 514 can operate atapproximately 80 psig and receive liquid from the bottom of thecontactor 512 and a vapor-liquid mixture from the ejector 534 from theflare gas recovery system 530. The flashed vapor can travel up the flashdrum tower 516 and be sent to boilers, where the gas is burned toprovide heat for another process. The liquid from the flash drum 514 canbe sent to the amine stripper 518 with a bottom operating pressure ofapproximately 15 psig and a bottom operating temperature ofapproximately 265° F. The circulation pump 520 can normally circulate atapproximately 9500 gpm with a discharge pressure of approximately 990psig. Approximately 7000 gpm of the amine solvent can be circulated backto the contactor 512 through cooler 522 such that 1200 gpm is sent tothe ejector 534 of the flare gas recovery system 530 and the balance isrecycled back to the suction of circulation pump 520.

In some embodiments, a portion of the flare gas from the flare header531 can be sent to the flare gas ejector 540, upstream of the seal drum532 for flashback prevention and liquid knockout. The lean amine solventand flare gas discharge 541 can be mixed within amine ejector 534 anddischarged as a vapor-liquid mixture back to the flash drum 514 of thegas sweetening unit 510.

The approximate flow rates and compositions of the streams can be:

Stream Number* units 511 513 519 521 523 525 529 531 Vapor flow MMSCFD600 — 2.79 — 63 — 535 2 Liquid flow gpm — 7000 — 8200 — 1200 — — Vaporcomposition mol % ** ** methane 70.0 — 90.6 — — — 78.4 85.5 ethane 6.0 —3.1 — — — 6.7 2.0 propane 2.5 — 0.0 — — — 2.8 — i-butane 0.5 — — — — —0.6 — n-butane 0.4 — — — — — 0.4 — i-pentane 0.4 — — — — — 0.4 —n-pentane 0.3 — — — — — 0.3 — carbon dioxide 5.0 — — — 48.0 — — 2.5hydrogen sulfide 5.5 — — — 52.0 — — 3.0 nitrogen 9.4 — 6.3 — — — 10.57.0 water 0.1 — — — — — — — *Refer to FIG. 5. **Composition is in drybasis.

In some implementations, a filtration package can be included to removeimpurities like salts or corroded materials that accumulate in thesolvent used for the gas sweetening process. The filtration package cancomprise a filter housing, a filter element or cartridge, an additionalcirculation pump, or a combination of multiples of these. Impuritiescollect on the filter element or cartridge as a fluid passes through thefilter. The filter element or cartridge can be cleaned or replacedperiodically.

FIG. 6 depicts a general schematic of a sixth exemplary system 600 thatincludes a primary gas sweetening unit 610 and flare gas recovery system630. The primary gas sweetening unit 610 of FIG. 6 comprises an aminecontactor 612, a flash drum 614, an amine stripper 618, an aminecirculation pump 620, an amine cooler 622, and an amine injector 634.The amine contactor 612 is a counter-flow gas-liquid contactor that canbe referred as an absorber, treater, or scrubber. The amine contactor612 is a vessel comprising internal components, which can include traysor packing, to increase gas-liquid contact.

The flash drum 614 operates at a lower pressure than the contactor 612and allows light hydrocarbons to flash (that is, evaporate) from theamine solvent. The flash drum 614 is sized for liquid surge, liquidholdup, and residence time for vapor to separate from the liquid aminesolvent. In some embodiments, the flash drum 614 is equipped with atower 616. The flash drum tower 616 can remove acid gas such as hydrogensulfide, which can be present in the vapor separated from the aminesolvent, before the vapor is sent to another downstream process or enduser.

Still referring to FIG. 6 , the amine stripper 618 is a vessel, whichcan also be referred to as a regenerator. The amine stripper 618comprises internal components, for example, trays or packing, andeffectively serves as a distillation tower to boil off acid gas toregenerate the amine solvent. The distinction between acid gas and sourgas is that sour gas is mostly hydrocarbons with some acidic gascontent, and acid gas contains little to no hydrocarbons.

The circulation pump 620 pressurizes the regenerated amine solvent torecycle the amine solvent back to the contactor 612. The circulationpump 620 can comprise a single pump or multiple pumps in parallel or inseries. The circulation pump 620 can be sized to accommodate upsetscenarios which require much higher flow rates than is normally requiredby the primary gas sweetening unit 610. The circulation pump 620, insome aspects, can employ a recycle line which routes a portion of theamine solvent back to the suction of the pump 620.

The amine cooler 622 brings the temperature of the solvent down beforethe solvent is recycled back to the contactor 612. The lower solventtemperature increases the efficiency of cleaning the sour gas thatenters the contactor 612. The cooler 622 can be a shell-and-tube heatexchanger, an air cooler, or a combination of multiples of both.

Gas sweetening units can optionally comprise auxiliary and variantequipment such as additional heat exchangers and vessels that have notbeen described above, but a majority of gas sweetening units across theworld implement some variation or combination of the major equipmentoutlined.

Gas sweetening units can operate at a variety of operating temperaturesand pressures. In some embodiments, sour gas at a temperature of between70-130° F. via stream 611 enters the bottom of an amine contactor 612,as amine solvent at a temperature of between 80-140° F. via stream 613enters from the top. The amine solvent that enters the amine contactor612 is at least approximately 10° F. hotter than the sour gas thatenters the amine contactor 612. As the amine solvent contacts the sourgas, the solvent removes (or “cleans”) the sulfur compounds, carbondioxide, and other contaminants from the sour gas, by chemical andphysical binding. Once the solvent has passed through contactor 612, thesolvent is considered to be in a “rich” state—also referred as “richsolvent”-because the solvent contains the hydrogen sulfide removed fromthe sour gas. The sweetened gas exits from the top of contactor 612 viastream 629, and rich solvent exits from the bottom via stream 615. Thesweetened gas (stream 629) can contain approximately 5-60 ppm hydrogensulfide and is sent downstream for sale or further processing. Richsolvent 615 is sent to a flash drum 614 operating between atmosphericpressure to 90 psig, where any flashed vapor travels up a flash drumtower 616 and exits via stream 619, where the flashed vapor can then beutilized as fuel, vented, flared, or a combination of these.

As shown, in this example implementation, rich solvent 615 can be sentto the amine ejector 634 and used as a motive fluid (discussed later)for the ejector 634 prior to (or in place of) being sent to the flashdrum 614 operating between atmospheric pressure to 90 psig, where anyflashed vapor travels up a flash drum tower 616 and exits via stream619, where the flashed vapor can then be utilized as fuel, vented,flared, or a combination of these.

Rich solvent liquid 617 from flash drum 614 is sent to an amine stripper618 with a top operating pressure between 5-17 psig. The hydrogensulfide and carbon dioxide is boiled off via heat input to the bottom ofstripper 618 operating between 230-270° F. in order to regenerate theamine solvent. The regenerated solvent is then considered to be in a“lean” state—also referred as “lean solvent”—that is once again suitableto be used for cleaning additional sour gas. Sour gas 623, comprisinghydrogen sulfide and carbon dioxide exits the top of stripper 618, andlean solvent 621 is pumped out of the bottom of stripper 618 bycirculation pump 620. Lean solvent 627 is cooled in heat exchanger 612to approximately 80-140° F. before re-entering contactor 612 to be usedagain to clean additional sour gas. The transport of vapor and liquidwithin, to, and from the gas sweetening unit 610 can be achieved usingvarious piping, pump, and valve configurations.

Still referring to FIG. 6 , the exemplary system 600 includes the flaregas recovery system 630 that is integrated with the gas sweetening unit610, as described above. The system 600 utilizes liquid rich aminesolvent 615 from the gas sweetening unit 610 as motive fluid for theamine ejector 634. The amine ejector 634 is positioned, in this example,within the gas sweetening unit 610. The amine ejector 634 comprises aninlet that continuously receives the rich amine solvent 615, whichserves as a high-pressure motive fluid from the gas sweetening unit 610via stream 615. The ejector 634 also comprises a gas inlet configuredfor receiving a stream 641 from the flare gas system 610 (as describedlater).

As illustrated in FIG. 6 , a flare gas ejector 640 is also included inthe flare gas system 630 and comprises an inlet that continuouslyreceives a lean or sour gas stream 642 (“gas stream 642”), which servesas a high-pressure motive fluid. The gas ejector 640 also comprises agas inlet configured for receiving a flare gas 633 as a low-pressuresuction fluid. The motive fluid operates at a higher pressure than thesuction fluid. For example, the gas stream 642 (motive fluid) operatesat approximately 990 psig, and the flare gas (suction fluid) operates atapproximately 0.5 psig. The motive and suction fluid mix within theflare gas ejector 634, and then discharge at an intermediate pressure tothe suction of the amine ejector 634 as flare gas stream 641.

FIG. 6 shows a certain implementation in which the discharge of theflare gas ejector 640 is supplied to the suction of the amine ejector634. The amine ejector 634 comprises an inlet that continuously receivesliquid rich amine solvent 615 from the gas sweetening unit 610, whichserves as a high-pressure motive fluid. The motive fluid operates at ahigher pressure than the suction fluid (flare gas stream 641). Forexample, the rich amine liquid solvent 615 (motive fluid) operates atapproximately 990 psig, and the flare gas stream 641 (suction fluid)operates at approximately 5-10 psig. The motive and suction fluid mixwithin the amine ejector 634, and then discharge at an intermediatepressure to the flash drum 614.

The type of system shown in FIG. 6 can also be applicable when thereexists at least two gas sweetening units operating at differentpressures. In some implementations, a booster pump is included toprovide adequate pressure to the amine solvent from the primary gassweetening unit 610 which is being utilized as motive fluid for theamine ejector 634, so that the recovered flare gas can be sent to asecondary gas sweetening unit.

System 600 can include a secondary gas sweetening unit (not shown, butsimilar to unit 150 in FIG. 1 , which includes a secondary aminecontactor 152), which operates at a lower pressure than the primary gassweetening unit 610. The amine ejector 634 can be installed near theflare header 631 and utilize rich amine solvent from a nearby gassweetening unit, such as the primary gas sweetening unit 610, as motivefluid to mix with and pressurize flare gas.

The flare gas recovery system 630 design takes into consideration theintegrated operation with the flare 670, which includes flashbackprevention 632. Flashback prevention involves preventing reverse flow ofgas and potentially, the flame from the flare, as flare gas 635 is beingburned at the flare 670. Flashback prevention can comprise a liquid sealdrum, a molecular seal, a fluidic seal, a flame arrestor, or anycombination thereof. The source of flare gas to the ejector 634 (oranalogous 234, 334) is upstream of the flashback prevention 632.

FIG. 6 provides a general schematic of a sixth exemplary system 600 thatincludes a gas sweetening unit 610 and flare gas recovery system 630. Asdepicted in FIG. 6 , the sweetening unit 610 is substantially the sameas the sweetening unit 110 of FIG. 1 , but the configuration of theflare gas recovery system 630 differs from the flare gas recovery system130 of FIG. 1 . Like element numbers across the figures can besubstantially the same; for example, the amine contactor 612 can besubstantially the same as the amine contactor 112. The amine ejector 634can be installed near the flare header 631 and utilize rich aminesolvent 615 from a nearby gas sweetening unit, such as the primary gassweetening unit 610, as motive fluid to mix with and pressurize flaregas 641. The two-phase mixture from the ejector 634 can be recycled backto the primary gas sweetening unit 610 and discharged directly back to aflash drum 614 via stream 637. The vapor phase can be separated fromliquid phase in the flash drum 614, because the both the liquid and gasfrom the ejector 634 are recycled back to the gas sweetening unit 610.Because flare gas is being recovered and recycled to the gas sweeteningunit 610, downstream units can require modification to accommodate theincreased vapor flow—for example, flash drum tower 616. The recoveredflare gas can then be utilized as fuel, vented, flared, or a combinationof these.

As shown in this example, a pressure reducing device 643, such as avalve or orifice, is positioned in the conduit for stream 615 betweenthe take-off to, and the return from, the liquid-driven amine ejector634. In some aspects, the pressure reducing device 643 may equalize (orhelp equalize) the pressure of the rich solvent 615 and the two-phasemixture 637 from the ejector 634 returning to the flash drum 614.

In some implementations, an additional circulation pump is included toprovide adequate flow of amine solvent from the gas sweetening unit 610,which is being utilized as motive fluid for the ejector 634.

Referring to the exemplary system 600 in FIG. 6 , in one example of thesystems described in this document, the amine contactor 612 of the gassweetening unit 610 can operate at approximately 980 psig. The leanamine solvent from the amine cooler 622 can enter the contactor 612 atapproximately 140° F., and the sweet gas (stream 629) can exit thecontactor 612 at approximately 120° F. The flash drum 614 can operate atapproximately 80 psig and receive liquid from the bottom of thecontactor 612 and a vapor-liquid mixture from the ejector 634 from theflare gas recovery system 630. The flashed vapor can travel up the flashdrum tower 616 and be sent to boilers, where the gas is burned toprovide heat for another process. The liquid from the flash drum 614 canbe sent to the amine stripper 618 with a bottom operating pressure ofapproximately 15 psig and a bottom operating temperature ofapproximately 265° F. The circulation pump 620 can normally circulate atapproximately 9500 gpm with a discharge pressure of approximately 990psig. Approximately 7000 gpm of the amine solvent can be circulated backto the contactor 612 through cooler 622 such that 1200 gpm is sent tothe ejector 634 of the flare gas recovery system 630 and the balance isrecycled back to the suction of circulation pump 620.

In some embodiments, a portion of the flare gas from the flare header631 can be sent to the flare gas ejector 640, upstream of the seal drum632 for flashback prevention and liquid knockout. The rich amine solvent615 and flare gas discharge 641 can be mixed within amine ejector 634and discharged as a vapor-liquid mixture back to the flash drum 614 ofthe gas sweetening unit 610.

The approximate flow rates and compositions of the streams can be:

Stream Number* units 611 613 619 621 623 627 629 631 Vapor flow MMSCFD600 — 2.79 — 63 — 535 2 Liquid flow gpm — 7000 — 8200 — 1200 — — Vaporcomposition mol % ** ** methane 70.0 — 90.6 — — — 78.4 85.5 ethane 6.0 —3.1 — — — 6.7 2.0 propane 2.5 — 0.0 — — — 2.8 — i-butane 0.5 — — — — —0.6 — n-butane 0.4 — — — — — 0.4 — i-pentane 0.4 — — — — — 0.4 —n-pentane 0.3 — — — — — 0.3 — carbon dioxide 5.0 — — — 48.0 — — 2.5hydrogen sulfide 5.5 — — — 52.0 — — 3.0 nitrogen 9.4 — 6.3 — — — 10.57.0 water 0.1 — — — — — — — *Refer to FIG. 6. **Composition is in drybasis.

In some implementations, a filtration package can be included to removeimpurities like salts or corroded materials that accumulate in thesolvent used for the gas sweetening process. The filtration package cancomprise a filter housing, a filter element or cartridge, an additionalcirculation pump, or a combination of multiples of these. Impuritiescollect on the filter element or cartridge as a fluid passes through thefilter. The filter element or cartridge can be cleaned or replacedperiodically.

Various modifications, alterations, and permutations of the disclosedimplementations can be made and will be readily apparent to those orordinary skill in the art, and the general principles defined can beapplied to other implementations and applications, without departingfrom scope of the disclosure. In some instances, details unnecessary toobtain an understanding of the described subject matter can be omittedso as to not obscure one or more described implementations withunnecessary detail and inasmuch as such details are within the skill ofone of ordinary skill in the art. The present disclosure is not intendedto be limited to the described or illustrated implementations, but to beaccorded the widest scope consistent with the described principles andfeatures.

Certain implementations of the subject matter have been described inthis document. Other implementations are, however, within the scope ofthe following claims.

What is claimed is:
 1. A method of supplying flare gas for a flare gasrecovery system, the method comprising: supplying, at a first positivepressure a flow of flare gas as a suction fluid from a flashbackprevention device to an ejector of the flare gas recovery system;supplying, at a second positive pressure that is at least two orders ofmagnitude greater than the first positive pressure, a continuous flow ofregenerable amine solvent in a rich state as a motive liquid to theejector from a primary gas sweetening unit that is in fluidcommunication with the flare gas recovery system; and combining theflare gas and the regenerable amine solvent in the rich state togetherin the ejector to form a two-phase fluid that comprises a mixture of thesuction fluid and the amine solvent in a lean state at a third positivepressure between the first and second positive pressures, wherein thecontinuous flow of the regnerable amine solvent in the rich state isconfigured to increase pressure of the flare gas to allow for deliveryof the two-phase fluid either directly or indirectly back to the primarygas sweetening unit.
 2. The method of claim 1, wherein the combining ofthe flare gas and solvent causes removal of a portion of one or morecomponents from the gas, the one or more components including at leastone of hydrogen sulfide or carbon dioxide, by at least one of chemicalbinding or physical binding, thereby resulting in the two-phase fluidcomprising of the solvent in the lean state and the gas suitable for oneor more of gas sweetening feed, combustion, venting, and flaring.
 3. Themethod of claim 1, further comprising filtering of the solvent to removeimpurities, the impurities including corrosion particles or salts. 4.The method of claim 1, wherein supplying the solvent in rich state isprovided by a pressure source, the pressure source comprising boosterpumps designated for the flare gas recovery system, to meet operatingconditions of a secondary gas sweetening unit.
 5. The method of claim 1,wherein supplying the solvent in rich state is provided by a pressuresource, the pressure source comprising circulation pumps in the primarygas sweetening unit or additional circulation pumps designated for theflare gas recovery system.
 6. The method of claim 1, further comprisingseparating the two-phase fluid into a rich solvent liquid phase and asweetened gas vapor phase.
 7. The method of claim 6, further comprisingcycling the liquid phase back to the primary gas sweetening unit, anddelivering the vapor phase to a secondary gas sweetening unit.
 8. Themethod of claim 1, wherein supplying the flow of flare gas to theejector comprises supplying gas from a main flare header, upstream ofthe flashback protection device.
 9. The method of claim 1, whereinsupplying the flow of flare gas to the ejector comprises supplying gasfrom one or more of emergency valves in the primary gas sweetening unitor a main flare header, upstream of the flashback protection device. 10.A method of supplying flare gas for a flare gas recovery system, themethod comprising: supplying a flow of flare gas as a suction fluid to aflare gas ejector of the flare gas recovery system; supplying acontinuous flow of a lean gas stream ora sour gas stream as a motivefluid to the flare gas ejector; combining the flare gas as the suctionfluid, and the lean gas stream or the sour gas stream as the motivefluid, together in the flare gas ejector to form a mixed gas fluid,supplying a flow of the mixed-gas fluid as a suction fluid to an amineejector of a gas sweetening unit; supplying a continuous flow of aregenerable amine liquid solvent in a lean state as a motive fluid tothe amine ejector from the primary gas sweetening unit that is in fluidcommunication with the flare gas recovery system; and combining themixed-gas fluid and the regenerable amine liquid solvent in the leanstate together in the amine ejector to form a two-phase fluid thatcomprises a mixture of the suction fluid and the regenerable amineliquid solvent in a rich state, wherein the continuous flow of thesolvent is configured to increase pressure of the mixed-gas fluid toallow for delivery of the two-phase fluid either directly or indirectlyback to the primary gas sweetening unit.
 11. The method of claim 10,wherein the combining of the mixed-gas fluid and solvent causes removalof a portion of one or more components from the mixed-gas, the one ormore components including at least one of hydrogen sulfide or carbondioxide.
 12. The method of claim 10, further comprising filtering of thesolvent to remove impurities, the impurities including corrosionparticles or salts.
 13. The method of claim 10, wherein supplying thesolvent in the lean state is provided by a pressure source, the pressuresource comprising circulation pumps in the primary gas sweetening unitor additional circulation pumps designated for the flare gas recoverysystem.
 14. The method of claim 10, further comprising separating thetwo-phase fluid into a rich solvent liquid phase and a sweetened gasvapor phase.
 15. The method of claim 14, further comprising cycling theliquid phase back to the primary gas sweetening unit, and delivering thevapor phase to a secondary gas sweetening unit.
 16. The method of claim15, wherein supplying the lean solvent is further assisted by anadditional pressure source, the pressure source comprising booster pumpsdesignated for the flare gas recovery system, to meet operatingconditions of the secondary gas sweetening unit.
 17. The method of claim10, wherein supplying the flow of flare gas to the flare gas ejectorcomprises supplying gas from a main flare header, upstream of aflashback protection device.
 18. The method of claim 10, whereinsupplying the flow of flare gas to the flare gas ejector comprisessupplying gas from one or more of emergency valves in the primary gassweetening unit or a main flare header, upstream of a flashbackprotection device.
 19. The method of claim 11, wherein the combining ofthe mixed-gas fluid and solvent comprises at least one of chemicalbinding or physical binding, the method further comprising: forming,based on the combining, the two-phase fluid comprising of the solvent inthe rich state and the gas suitable for one or more of gas sweeteningfeed, combustion, venting, or flaring.
 20. The method of claim 2,wherein supplying the solvent in rich state is provided by a pressuresource, the pressure source comprising booster pumps designated for theflare gas recovery system, to meet operating conditions of a secondarygas sweetening unit, and supplying the solvent in rich state is providedby a pressure source, the pressure source comprising circulation pumpsin the primary gas sweetening unit or additional circulation pumpsdesignated for the flare gas recovery system.